If you already filed your federal return and it's been accepted, you can amend your 2016 return by following these steps:
- Sign back
     in to TurboTax and go to your Tax Timeline.  [See Screenshot #1,
     below.]
- In the
     section Some Things You Can Do (below the grey line), click on Amend
     (change) return. [Screenshot #2] 
- On the screen,
     Are you sure you'd like to amend, click the box Amend using
     TurboTax Online. 
- On the
     screen, Have you already filed this return, click the Yes
     button and then click the button next to I need to amend my 2016 return
     and click Continue.  [Screenshot #3 ] 
- On the
     screen, What do you need to change on your return, scroll down and
     click on the Update box next to the Personal Info & Dependents. [Screenshot #4]
- When on the Personal Info Summary, click on the box Add a dependent.  [Screenshot #5]
 
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